The instant invention relates generally to medical tools and more specifically it relates to a non-reusable, single use hypodermic syringe. Because diseases such as AIDS are easily transmitted between individuals by the reuse of hypodermic needles, there is a vital requirement for a hypodermic syringe which permits only one time use. It is this requirement that the instant invention is designed to satisfy.
Numerous medical tools have been provided in the prior art that are adapted to help in the assistance in treating various illnesses and injuries to people. While these units may be suitable for the particular purpose which they address, they would be as suitable for the purposes of the present invention as heretofore described.
There are several hypodermic syringe constructions with non-retractable drive pistons. One such prior structure is that identified in U.S. Pat. No. 4,391,272 entitled "Disposable Syringe", issued to Jackie Staempfli which discloses a segmented disk 6 attached to a plunger 4 lockable in annular grooves 5 so that the plunger 4 is capable of being moved forwardly with minimum resistance between disk 6 and the inner wall of the cylinder, but when the plunger is moved fully forward, disk 6 is locked in groove 5 preventing upwardly rearwardly movement of the plunger.
U.S. Pat. No. 4,493,703 issued to Ida M. Butterfield entitled "Hypodermic Syringe Cartridge With Non-Retractable Piston" illustrates another resilient disk-like element 32 which is flexed rearwardly permitting the plunger to move forwardly in the barrel. Disk-like element 32 is captured in annular grooves formed by a ratchet surface formed on the inner wall of the barrel. In this manner, the flexed disk-like member 34 prevents rearward movement of the plunger, including the additional resistance to movement required to force the disk-like member from its pre-stressed rearwardly flexed position.
U.S. Pat. No. 4,979,943 issued to Lewis E. Trenner entitled "Single Use Hypodermic Needle" illustrates yet another form of lock to prevent retraction of the plunger after dispensing of the fluid through the syringe by providing a reversal stop 86 which bears against end wall 16.
Each of these prior art devices requires that the groove which locks the disk from rearward movement be substantially perpendicular to the axis of the plunger. Since swinges can be of varying sizes, a square shaped groove may not easily be achievable for one cc. syringes. The thickness of the barrel and the tolerances achievable do not allow for sufficient accuracy to produce reliable syringes of such small sizes. Further, the manner of preventing reverse movement of the plunger merely relies upon the mating bearing surfaces between the rear wall of the disk and front wall of the seat formed by the groove. be possible to actually use sufficient force to bend the disk and pull it out of the groove allowing the plunger to be removed from the barrel.